1. Field of the Invention
The present invention relates to a method and an apparatus for the sealing of glass tubes in a hot softened state, especially of glass tubes, which are intended for the production of primary packaging means made of glass for the storage of pharmaceutically active substances.
2. Description of Related Art
In the production of glass tubes usually glass tubes are severed from the glass tube line (glass tubing), which are then processed further. These glass tubes may have standard lengths of e.g. 1.5 m, but may also be severed off to relatively short glass tubes of a few centimeters in length in order to be processed directly to primary packaging means for the storage of pharmaceutical substances, for example, glass ampoules, glass vials or glass syringes. Particularly for the latter applications, it is indispensable that no impurities reach the interior of the glass tubes in the course of processing and handling, as these can be removed from it again only with considerable effort.
Therefore, the tube ends are severed off in a hot softened state directly at the glass tubing in a special tube end processing machine and the tubes are sealed therewith to prevent a deposition of particles inside the glass tube.
In the known methods, the tubes are usually processed individually on rotating rollers, and the glass tube is separated by heating an annular zone and subsequently moving apart of the roller units.
GB 174049 A discloses a device, in which the glass tube is rotated continuously about the longitudinal axis by pairs of rollers. A burner, which is arranged near the peripheral edge of the glass tube, heats the rotating glass tube until it is sufficiently softened. In the hot softened state of the glass tube the pairs of rollers are pulled apart along the longitudinal axis of the glass tube to sever the glass tube. Thereby the edges are fused to a flat bottom at the end portions of the glass tube so as to seal the end of the glass tube. The contact pressure which is necessary for enabling the pairs of rollers to rotate the glass tube evenly, however, causes a risk for cracks and scratches. The contact surfaces are therefore potential sources for contamination and abrasion.
According to DE 1114992 A, the glass tubes are grasped by holding means and conveyed along a vertical conveying path by means of a vertical conveying device and thereby heated by means of a plurality of annular softening burners. Rotating tongs grip the softened end portions of the glass tube and are pulled apart. The severing of the end portions in a hot softened state is further assisted by means of side-mounted obstacles, such as knives. However, due to the conveyance in the vertical direction, breaking tubes or pieces thereof fall down on subsequent glass tubes, which can lead to breakage or damage to the glass tubes.
DE 1127042 A discloses a further method, in which the glass tube is put in a uniform rotary movement by means of several pairs of rollers which engage the respective end of the glass tube. A gas flame softens the severing zone, while the glass tube is rotated. An additional obliquely-positioned roller pulls the respective end portion axially from the glass tube. At the same time the gas flame fuses the end portion to a flat bottom. Due to tolerances of the glass tube, fluctuating friction conditions and sliding effects, however, ambiguous and fluctuating movements or even wobbling movements may occur and thus varying results at the sealed end of the tube may occur. Since the glass tubes are processed, clocked relatively little time remains for processing.
DE 19908342 C1 discloses a further method, in which a screw, which is mounted coaxially to the glass tube, is rotated synchronously to the conveying movement of the glass tube in such way, that the peripheral edge of the screw reaches the outer surface of the glass tube at a certain point of engagement and is wandering around the glass tube in an axially perpendicular plane to sever off the glass tube. The end of the glass tube is, however, not pulled off.
EP 1834931 A2 discloses a method for melting the ends of glass tubes. For this purpose, a longer glass tube is first cut into relatively short glass tubes, which are then deposited on a gripping chain. In doing so, the ends of the tubes are freely accessible from the side. The glass tubes are guided via a lifting rail and lifted thereby. During the subsequent rolling on the lifting rail the glass tubes are caused to rotate, while the end of the glass tube is fused by a gas flame. A sealing of the end of the glass tube is not disclosed.
U.S. Pat. No. 2,633,672 A discloses a method for the sealing of glass tubes in a hot softened state for the production of vials, in which these are moved along a conveying path and put in a uniform rotation about their longitudinal axis by moving rubber bands. Thereby the axis of rotation of the vials is stabilized by means of a cylinder. The rotating vials are moved along a strip of burners and heated and softened evenly around their circumference. At the same time the neck portion softens, which is pulled off axially by a rotating finger having a U-shaped hook, so that the end portion is fused and the vial is sealed by a plug. To put the glass tubes in a uniform rotation, a considerable effort is required. The sealing of the end of the glass tubes by means of a simple plug is unsuitable for many applications.